How the Height of a Geocell Affects Soil Reinforcement
Geocells are used in many projects to reinforce and stabilize soils. They also serve as a protective lining for footings. In addition to their structural benefits, they help reduce surface heaving.
The height, width, and pocket opening size of the geocell play a critical role in the reinforcing action. Various mechanisms that are responsible for this action include confinement, stress dispersion, and lateral resistance.
Optimal Geocell Height
The height of a Geocell affects its performance and the effectiveness of soil reinforcement. It has been shown that the shear strength of geocell-reinforced soil increases with decreasing pocket size up to a certain optimum value and stabilizes thereafter [22] [23]. This behavior is attributed to increased confining stress in the confined sand due to smaller cell surface area. This increased shear strength offers better footing performance by reducing controlled settlements and heaves and increasing the traffic benefit ratio (TBR) [24].
The shear strength increment caused by geocells with smaller pocket opening diameter is more significant than that produced by the same soil without any geocell. The increment reaches up to 31% when the failure plane passes through the center of the geocell height. In contrast, a shear test performed with a geocell placed far away from the failure plane shows that the increase in shear strength is reduced by around 5%.
In addition, the position of the failure plane relative to the center of the geocell height also influences the shear test results. When the failure plane is tangential to the geocell height, shear tests produce results that are comparable to those of unreinforced soil. Conversely, when the failure plane is farther from the geocell height, shear tests result in significantly lower shear strengths compared to the unreinforced soil.
Optimal Geocell Width
Since geocells act as composite beams, they distribute the footing load across a wider area. This improves the stability of soil, which minimizes the differential settlement and overall settlement of the bridge deck compared to unreinforced sections. Additionally, it reduces the number of cyclic loading cycles needed to achieve the desired traffic benefit ratio.
The initial studies on the use of geocells as a bridge deck reinforcement were performed Height Geocell using circular or square-shaped geocells [1]. However, the current commercially available geocells are honeycomb shaped to enclose maximum infill material within a minimum perimeter of cells. This shape also enables the cells to collapse during transit and handling for easy storage.
In addition to the optimum geocell height, the size of the confined sand area, pocket opening diameter, and the aspect ratio are essential factors for a successful geocell application. Moreover, the geometry of the sand cushion must be considered to ensure that the shear stress reaches the optimum value.
A simulated direct shear test was conducted on three quadrangular geocells with different heights and pocket opening diameters, where the predetermined failure plane crossed through the middle of the geocell height (Fig. 4). The ABAQUS software was used to simulate the test in a three-dimensional state. The modeling results indicated that shear strength improvements of geocells were dependent on the aspect ratio and pocket opening diameter, but not on the height increment.
Optimal Geocell Aspect Ratio
Geocells are an efficient alternative to conventional geogrids in soil improvement projects. They offer a more reliable performance than conventional geogrids due to their multi-dimensional geometry, which redistributes the load in a wide area and improves the apparent cohesion of the infill soils [16]. In addition, geocells provide all-round confinement and enhance the bending rigidity of a structure.
The aspect ratio of a height geocell refers to the ratio between its height and its pocket opening diameter, which is an important factor that determines the shear resistance of the geocell-reinforced soil. It is reported that a larger ratio of height to pocket diameter improves the performance of geocells. This is because a smaller pocket diameter results in more pockets and increases the confined sand area at the interface with the soil, thus improving the interfacial shear strength of the reinforced soil.
Moreover, the presence of more layers in the geometry of geocells also has an impact on their shear-strength capacity. Kargar and Hoessini conducted model tests to study the effects of two- and four-layered geocells on the shear capacity of a soil bed. The results showed that a chevron pattern of geocells offered greater shear rigidity than a diamond pattern, even at large settlements.
The chevron pattern of the geocells provides more flexural rigidity for the same plan area of the geocells as compared to a diamond pattern, which requires connections involving three grids. This is because a chevron-patterned Height Geocell geocell has more joints than a diamond-patterned one, which allows the geocell infill to be stiffer under unsaturated conditions.
Optimal Geocell Pocket Diameter
The height, width and pocket opening size of the geocell are all factors that affect its performance. The height of the geocell, in particular, is a crucial parameter that plays a significant role in its reinforcement mechanism. When a shear test is performed on the geocell, the soil pushes against the cell walls and develops an additional confining stress that prevents the soil from lateral movement and increases its shear strength. The height of the geocell also influences the shear resistance of the soil-geocell interface, and a proper understanding of this phenomenon can help engineers optimize the design of geocells.
A variety of tests have been conducted on geocells, including shear tests and cyclic loading tests. The results of these tests show that the performance of the geocell improves with a decrease in its height and pocket size. However, the improvement in performance reaches a threshold value after which it stabilizes or declines.
In order to understand the optimum height of the geocell, various studies have been performed on the behavior of the shear-reinforced soil using ABAQUS software. The failure plane of the shear box was positioned to pass through the center of the geocell height, and the test results were evaluated based on the slope of the shear stress-horizontal displacement curves. It was found that the shear resistance of the soil-geocell-reinforced layer increased as the distance between the shear plane and the geocell-height increased.